Fe (hydro) oxide controls Mo isotope fractionation during the weathering of granite

作     者：Wang, Zhibing Ma, Jinlong Li, Jie Wei, Gangjian Zeng, Ti Li, Lei Zhang, Le Deng, Wenfeng Xie, Luhua Liu, Zhifeng 

作者机构：Chinese Acad Sci Guangzhou Inst Geochem State Key Lab Isotope Geochem Guangzhou 510640 Guangdong Peoples R China Chinese Acad Sci Guangzhou Inst Geochem CAS Key Lab Marginal Sea Geol Guangzhou 510640 Guangdong Peoples R China Chinese Acad Sci Xinjiang Inst Ecol & Geog Xinjiang Key Lab Environm Pollut & Bioremediat Urumqi 830011 Peoples R China 

出 版 物：《GEOCHIMICA ET COSMOCHIMICA ACTA》 (地球化学与宇宙化学学报)

年 卷 期：2018年第226卷

页      面：1-17页

核心收录：

学科分类：0709[理学-地质学] 081803[工学-地质工程] 07[理学] 08[工学] 0708[理学-地球物理学] 0818[工学-地质资源与地质工程] 

基　　金：National Natural Science Foundation of China [41325012, 41473019, 41703011] Guangzhou Science Technology and Innovation Commission GIGCAS 135 Project [Y234091001] GIGCAS [IS-2501] 

主　　题：Molybdenum Isotopic fractionation Fe (hydro)-oxide Granite weathering Adsorption and desorption Sequential extraction Clay mineral 

摘      要：Understanding the fractionation mechanisms of Mo isotopes and seeking the main hosts of light delta(98/95) Mo during chemical weathering of continental rocks is a prerequisite for constraining heavy delta(98/95) Mo input into rivers. This study investigates the Mo concentrations and delta(98/95) Mo values of bulk samples, chemical extractions, and clay fractions of weathering products in a granite weathering profile in Guangdong province, South China, as well as in surrounding stream water. Results from bulk samples show that the tau Mo-TiO2 values systematically decrease from 59.1% to -77.0%, and delta(98/95) Mo values systematically increase from -1.46% to -0.17%, upwards in the profile (from 30 to 0 m depth). Atmospheric input has a limited effect on delta(98/95) Mo variations in the weathering profile. Adsorption and desorption processes of Fe (hydro) oxide are the dominant factors controlling the variations in delta(98/95) Mo, with light Mo isotopes preferentially adsorbed by Fe (hydro) oxide, and released during desorption process, whereas the incongruent dissolution of primary minerals has little effect. Organic materials and the clay fraction are not the main hosts of light delta(98/95) Mo, as indicated by the results of chemical extractions, which show that a large proportion (41.5-86.2%) of total Mo with light delta(98/95) Mo (-1.57% to -0.59%) is associated with Fe (hydro) oxide. Moreover, a significant positive correlation exists between Mo concentrations and delta(98/95) Mo in the Fe (hydro) oxide extractions from bulk samples. Finally, delta(98/95) Mo in stream water indicates the release of heavier delta(98/95) Mo into river water during the chemical weathering of granite rock. The results advance our understanding the mechanisms of Mo isotope fractionation during chemical weathering and its isotopic mass balance in Earth s surface system. (C) 2018 Elsevier Ltd. All rights reserved.